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Your Energy/Cooling Vocabulary
Some time soon you will be discussing power and cooling technologies. IT staff will have to pay attention to the power and cooling bill since it is becoming a significant part of the everyday IT expenses. In the data center, 50% of the power bill drives the IT equipment and 43% of the power bill is for cooling that IT equipment. The other 7% supports lighting, signs, etc.When you read the power requirements for IT equipment, do not use the numbers in the specification sheet. These numbers are average consumption and usually do not reflect real use. Here are some of the variations you will encounter when determining the actual power used.
* There are major power consumption differences for IP Telephony call managers, up to 50% difference.
* Routers and LAN switches have a chassis that consumes power no matter how many ports are attached. This can vary as much as 50% from vendor to vendor.
* Routers and LAN switches consume power for every port that is implemented.
* Ports may consume less power if no cable is attached.
* PoE power will depend on the endpoint, whether it is a class 1/2/3 device and how the LLDP or CDP allocates power.
* PoE supporting 802.3at will consume more power than 802.3af.
* 1GBE cards consume more power than 10/100mbps cards.
* The amount of traffic passing through the router or LAN switch can affect the power consumption.
* Go to www.tolly.com for full test comparisons of call managers, routers and LAN switches operating in real traffic configurations. Some comparison tests exercised eight different port and traffic configurations.
Here is a short vocabulary of the terms that may be mentioned when discussing energy costs and how to control and reduce them. Use this blog as a reference.
Amp--It is a basic unit of electric current. It is defined as the total net charge flowing across a given cross-sectional area of wire per second.
BTU--British Thermal Unit; the heat required to raise one pound of water one degree Fahrenheit.
CFM--Cubic Feet per Minute. Higher CFM carries more cooling air, but the CFM can be limited by the cooling duct size.
Demand (kw demand)--The maximum number of kilowatt-hours per defined time interval (hour). This is commonly based upon the largest number of kilowatt-hours used in any half-hour or fifteen-minute period of the billing period. Demand charges reflect the electric utility's infrastructure cost of power generation and transmission. There is normally a cost to the enterprise for the size of the infrastructure connection independent of the amount of power actually consumed. Demand equals the size of the electrical pipe to the enterprise building.
EER (Energy Efficiency Ratio)--This is a measure of how efficiently a cooling system will operate when the outdoor temperature is at a specific level (usually 95°F). A higher EER means the system is more efficient. EER equal to 10 is best.
EMS (energy management system)--This reduces the energy use in buildings by monitoring conditions and controlling energy consuming equipment.
Horsepower (hp)--This is a unit of power, typically associated with motors, One hp = 746 watts. Kilovolt-Ampere (KVA)--This is a unit of electrical power equal to 1,000 volt-amperes
Kilovolt-Ampere Reactive (KVAR)--The electric utility must supply more power than the enterprise actually uses to account for the energy losses in the transmission facilities.
Kilowatt Demand (kW demand)--The maximum number of kilowatt-hours per defined time interval used. This is based upon the largest number of kilowatt-hours used in any half-hour or fifteen-minute period of the billing period.
Kilowatt-Hours (kWh)--The quantity of true power multiplied by time. 1,000 watts of power used for one-hour equals one kilowatt-hour.
Load Factor--The ratio of the average electrical load divided by peak load during a designated period of time. As an example, if a business used 20,000 kWh during one month (720 hours) and had a maximum demand of 50 kW, then the load factor would be 55.5 percent (20,000 kWh x 100)/(720 hours x 50 kW).
Power Factor (PF)--This is a ratio equal to the real power (kW) divided by the apparent power (kVA). PF = kW/kVA If the PF is less than 95%, most utilities will charge the enterprise an additional fee because the low PF causes wasted energy.
SEER (seasonal energy efficiency ratio)--This is a measure of efficiency over an entire cooling season, as opposed to a single outdoor temperature. SEER is the total amount of cooling the air conditioner provides over the entire cooling season divided by the total number of watt-hours it will consume.
Three-Phase Power (3 phase)--This is a very efficient means of transmitting electrical energy when compared to single phase power that drives many of the smaller IT devices.
Ton (refrigerant ton, RT)--A ton is defined as the cooling capacity of an air conditioning system. One ton is equal to the BTU thermal content required to melt one ton of ice in a 24-hour period.
Volt--This is the electrical potential the basic unit of voltage, or electric potential difference.
Watt--This is a measure of power that is the product of voltage (volts) and current (amps). It is roughly equivalent to 3.412 BTU/hr.